1. Field of the Invention
The present invention relates to a post-processing apparatus for applying a specified post-processing to sheets fed from an image forming apparatus such as a copier, a facsimile apparatus or a printer.
2. Description of the Related Art
There have been known post-processing apparatuses as disclosed in Japanese Unexamined Patent Publication No. 2002-128382. This post-processing apparatus is for applying punching to perforate binding holes in sheets fed from an image forming apparatus, and stapling to bind a stored bundle of sheets. Such a post-processing apparatus has a punching machine, a staple tray, a standby drum and a switching guide built in an apparatus main body. The punching machine is disposed at an intermediate position on a receiving conveyance path for receiving a sheet from the image forming apparatus to apply punching to the sheet. The staple tray is disposed below the receiving conveyance path to form a bundle of sheets by temporarily storing the sheets fed from a downstream end of the receiving conveyance path and to apply stapling to this bundle of sheets. The standby drum is disposed above the downstream end of the receiving conveyance path to temporarily store sheets to constitute a next bundle of sheets while stapling is applied to the previous bundle of sheets on the staple tray. This standby drum stores sheets on its outer circumferential surface. The switching guide is disposed at the downstream end of the receiving conveyance path to switch a conveyance end of the sheet between the staple tray and the standby drum.
The standby drum is disposed at such a position as to enable an operation of temporarily storing the next sheets while the previous bunch of sheets is temporarily stored on the staple tray to be stapled, and supplying the sheets kept on standby to the staple tray after the previous bunch of sheets was discharged after the completion of stapling. This operation enables conveyance intervals of the sheets fed from the image forming apparatus to be kept constant, thereby making the image forming operation including the post-processing more efficient.
The staple tray is comprised of a lower tray obliquely disposed in the apparatus main body and an upper tray disposed to face the upper surface of the lower tray. A storage space for storing the sheets is defined between these upper and lower trays. Stapling is applied to the bunch of sheets stored in this storage space by means of a stapler, and the thus obtained bound bunch of sheets is discharged from the storage space toward a discharge tray located outside.
In order to easily solve a problem of a paper jam during the stapling, the staple tray is made withdrawal from the apparatus main body in a sheet-width direction normal to a sheet conveying direction. The upper tray in a withdrawn state is pivotal about a specified position at the bottom end of the lower tray to open up the clearance. Accordingly, when a paper jam occurs, an operator can expose a jammed position to the outside by opening the upper tray, wherefore the paper jam can be easily solved.
In the post-processing apparatus disclosed in Japanese Unexamined Patent Publication No. 2002-128382, the standby drum for temporarily keeping the sheets on standby is disposed above the receiving conveyance path. In order to temporarily store the sheets by letting the sheets wind around the outer circumferential surface of the standby drum, a considerably large diameter needs to be set for the standby drum. If such a standby drum is disposed at an upper part of the apparatus main body, there arises a problem of increasing the height of the apparatus main body and hindering the post-processing apparatus from being made smaller.